1. Field of the Invention
The present invention relates generally to the field of load sensors and more particularly to a washer having strain gauges for measuring axial forces applied to the washer.
2. Background Art
There are numerous applications where it would be highly advantageous to be able to measure axial load in a washer. For example, such a capability would permit extremely accurate application of clamping forces produced by a nut and bolt assembly of which the washer were a component. Another example is for measurement of the load on a hook supported by the washer in combination with a nut or other fastener. The use of strain gauges to measure force applied to a structure is a well-known application. By way of example, U.S. Pat. No. 5,872,320 discloses a force transducer which may be used in a computer keyboard to control the position of the cursor on a display screen. As shown in that patent, the strain gauges are typically configured in a bridge arrangement. Connecting the strain gauges in a bridge circuit provides a larger signal swing which results in greater resolution and also renders the output signal relatively insensitive to temperature variation which could otherwise alter the characteristics of the transducer with changes in ambient temperature.
Use of strain gauges in a small mechanical device like a washer, the entire structure of which is subjected to substantially the same axial forces, makes it difficult to connect strain gauges in a bridge configuration and thereby achieve the advantages of greater output signal amplitude swing and temperature insensitivity.
It would be highly advantageous if it were possible to provide a washer with strain gauges configured in a bridge arrangement where the performance improvements of true bridge operation could be realized.